Best, What Up? What Up? What Up? Everybody? Welcome to
another episode of Let's Ask Paul, the podcast where you get to ask me
Paul Abernathy anything you want about the National Electrical Code and all things electrically related.
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Okay, so let's look at our first question that we have. Then,
this one was submitted to me actually over on LinkedIn, and that's somebody that's
preparing for an electrical exam. I believe. I don't think they're a student
of ours, but they're preparing for an electric exam and they ask a question.
So I'm gonna read the question and try to break it down. I
will tell you upfront, I am not the best educator in the world when
it comes to the Ohms law, Watts law stuff. I teach it,
I understand it. I can help you pass an exam, but I am
not the best theorist in the world. Okay, So I do my best,
but let me explain it to you. So let me read the question
and then hopefully it helps some of you out. Okay, the question says
mister Abernethy. I hope you're doing well. I'm a journeyman preparing for my
contractor's exam, and there is an electrical theory question I have that is really
making me scratch my head. With Ohm's law, i equals E divided by
R, current is directly proportional to voltage, meaning that the voltage rises and
your amps will also rise. That is correct in Ohm's law dealing with the
fixed resistance value, that's correct, says. Yet if you use I equals
P which is wattage, or power divided by E which is voltage, your
current is inversely proportional. That is correct as well, because you're trying to
maintain a certain power level. Right. So in the field, it has
always been that the higher the voltage would give you, the lower the current.
That's because you're using the power formula of example, would be primary and
secondary of a transformer, dual voltage pump, et cetera. So these are
power values, va being the equivalent to wattage. Especially if you're used to
doing calculations and whatnot, you don't necessarily use Owns law, which is resistance.
Maybe for an exam, but in the real world you very rarely use
the OHMS law. Usually use the power formula for most of the things that
you do, although we'll talk about analogies and I'll give you some scenarios,
but mainly the reason you're getting that is because you're probably doing something with a
fixed load, a fixed VA or fixed wattage, and you're using a power
formula calculation, and that's where you're going to have the higher voltage lower current.
Okay, so it's inversely proportional. So anyway, it says, I
don't fully understand how simply changing the voltage in both applications will cause your amps
to rise in one and fall in the other. In a short brief explanation
here, understand that what you're doing here is with one it's directly proportional to
the resistance, so that doesn't change. So as the voltage goes up,
the current goes up, the voltage didn't change. Okay. When it comes
to the power formula, the wattage or the need for a certain amount of
power stays the same. It's fixed. What you're doing is you're changing the
voltage, and by doing so, in order to regulate it so that the
wattage that you need the power that you need doesn't change, then you're going
to have to do something. And that's why it's inversely proportional. That means,
if you increase the current I mean, excuse me, it increase the
voltage, then the current must come down in order to maintain the same level
of power. Okay, so that that value doesn't change, because if you
need six hundred watts, you need six hundred watts. You get what I'm
saying. So most people get those two confused. Between the owner's law,
where you're dealing with a fixed resistance value maybe versus a power formula where you
have a certain load or certain power that you need to work with and then
you will adjust the voltage in order to you know, get a different current,
but you're trying to maintain the power level or the work that needs to
be done. So that's probably the reason that you see these differently, and
I would think mainly in the real world you're probably working more with power formula
than you are with a Ohm's law pure resistance. It says I don't fully
understand how Okay, we already read that, and says, could you please
do me a favor and simplify this and make a video better explaining this to
a simpleton like myself. I don't think you're a simpleton at all. I
think this is something that people get lost in wanting to know why the theory,
you know, And I like to tell people, I'm no Thomas Edison,
I'm no Einstein, I'm no Tesla. There's basic concepts that we've had
for eons and you just have to embrace them. And I probably do a
poor job at explaining the indepthness of it, but I can show you the
relationship and why, and basically give you the understanding that if the wattage is
fixed or the resistance is fixed, then changing the voltage can really can change
what the current is. So if you're dealing with a certain power, you
need wattage certain power, then again, increasing the voltage is going to decrease
the current, Whereas if you're dealing with pure resistance that's fixed, if you
increase the voltage, you're increasing the current. Okay, And I'll give you
some analogies of that so you can get an understanding. So that'll take us
into that. Okay, Okay. So the first thing we want to do,
though, is let's go on and talk about some things that are key
concepts that you need to be aware of. And I'll even use some analogies
to water and things like that to just try to make it as simple as
possible. I will do my best in a podcast. And the reason I
use podcasts for these type of things and not videos is because it forces me
to try to explain something verbally to paint a mental picture, and it's basically
keeps it interesting for me, keeps it fun for me because it allows it
forces me to try to explain things in a way that maybe when you hear
it, it'll go, oh, I get it, and maybe the light
will come on. Okay, So let's look at the relationships here. Some
key concepts. So voltage, which is expressed in many formulas, is V
for voltage or even E okay for voltage, depending on what formula you're using.
So talk about voltage. What is voltage? Well, voltage is the
electric potential difference between two points. Okay, it is the push Okay if
you will, It's the pressure that drives electric charges electrons through a circuit.
Now, similar to that would be an example of water pressure. You increase
your pressure, you increase your voltage. If you increase your water pressure.
You're gonna be pushing water through a pipe. If you increase the pressure,
you're gonna push it. Now, voltage is measured in volts, and we
usually will use a V or in your owns wheels and things like that,
we use the letter E. Okay, but just remember if you see V,
that's voltage. Now. Current is given to us in the letter I,
and it may be an A for amps. But current current is the
flow of electric charges through a conductor such as a wire. Doesn't have to
be a wire, Okay, there's other conductors of electricity, but think of
it as a wire because you're electricians. It's the current, the flow of
electric charge that is moving through that conductor of the wire type. Let's just
say for this example, so it is kind of like the flow of water
through a pipe. As that water flows, you increase the voltage, more
pressure pushes more water through faster. Okay, But that flow of water,
that movement of that flow of electric charge through a conductor is very similar to
like the flow of water. So that's why you hear people talk about this
analogy of water, Okay, because they're trying to paint a picture that's easier
to understand. And of course current is measured in ampeers. We refer to
that as amps short or maybe even just an A, depending on what your
formula you're working with, or where you get it from, what school you
may be studying in, or whatnot. So next one is resistance, which
you know, could be an own symbol okay omega, could be just R,
and that represents resistance, well, resistance exactly how it sounds. It's
the resistance or the opposition to the flow of current in a circuit. Now
think of this analogy again that we've been talking about a water hose or a
pipe. So it's like the friction on the sides of the pipe. It's
the friction that that water would experience as it's flowing through a narrow or even
a pipe that is rough, you know, filled with all kinds of build
up, calcium, whatever. So what happens is it's restricting the flow.
Now this restriction is again measured in ohms. We use the OM symbol omega
okay, Greek symbol. But again, resistance is the opposition to the current
flow. Now, if you think about that in a conductor and you go
to chapter nine, Table eight for example, and you look at resistance DCE
resistance, then you're going to see that as the conductor gets bigger, it's
kind of like a bigger pipe and the resistance goes down, thus means it
carries more current, right, it is less resistance a current flow. Okay,
so that's the analogy we use in resistance. So just think of resistance
and it would also be an example of somebody taking a garden hose and then
they pinching it or squeezing it, and you reading the overall size of it.
The orifice gets smaller, so that is restricting or opposition to current flow.
Right, So that's resistance, and there is resistance in all of a
conductor, but in a pipe order pipe, the resistance is the friction along
the surface of the piping system adds to the resistance of the water flow,
which is again all again opposition to the flow. That's resistance. Next one,
the last one we'll talk about when it comes to the concepts. Here
is power and that is p for power and you may see this on some
formulas as a way which power is usually expressed in watts. And of course
one thing to remember when we're doing load calculations that va volt damp years is
synonymous with wattage. Y'all know when we do range calculations and you see eight
thousand va, and it's the same as eight thousand watts. So in that
case, so again that's power. Okay. So it's obviously not given to
us in a resistance value. It's given to us in power. So with
that said, there's one important thing to us to understand that there are such
things as Ohm's law, right, and there's such things as power formulas.
And you might have an Ohms wheel, and your Ohm's wheel will have all
kinds of equations on it, right, Oh gosh, it'll it'll have watts,
uh, It'll have volted lambs and the Ohms. And this is basically
a power wheel. And of course within this power wheel you'll get your your
you'll have your basics Ohms law equations. And the basic Omes law again is
current E equals I mean, excuse me, current I equals E or V
divided by R the resistance, or to solve the resistance, it is E
for voltage or V for voltage divided by I the current. And of course
if you're trying to find the voltage, then it would be I. The
current times are the resistance. So that is your basic OMES formula. Okay,
so that's the formulas lose Now when you start getting into a little deeper,
then you start getting into what we call power formulas and the power.
One of the power formulas we have is P, which is power equals V
or E for voltage times I which is the current. Course, the same
scenario comes into play if you're doing it where you want to find the current,
but you know what the power is, then it's pretty simple, right
then it would be P divided by the voltage to find the current. Makes
sense. So you have all these different formulas that you would use, and
a good on wheel is going to give you ohms and power in everything in
it. We call that a power formula wheel. Whereas a typical OMS would
be a circle with the line through the middle, so you have a top
half and a bottom half, and then from that middle line you draw a
line straight down in the middle, so basically gives you three quadrants, okay,
and you get two on the bottom and one big one on the top.
Well, in the top one you would put the E or V for
voltage okay, and then on the bottom you would put an I on the
left side that would be for current, and on the right you'd put an
R for resistance. So if you put your finger over any one of those,
then you would follow the If you put it over the I, then
would be E divided by the R. If you put it over the the
R, then it would be E, which is on the top divided by
the I, which is on the bottom left. Or if you put it
over the E the top portion, then it would be the I in the
R. Excuse me, the the the I in the Yeah, the E
I R the I in the R would be side by side, so that
would be your current times the resistance. So E I R I don't know
if I said that right earlier, but that's what you would get for that.
And it's the same thing for PI or the power wheel. If you're
just simplifying it down, same circle, same way you make it, but
instead of it being E I R, it's P I E. So P
goes on the top, I goes on the bottom left, and then E
goes in the right. So if you're solving for power, it's just II
the current times E the voltage or V the voltage. If you're solving for
a current, then it would be power divided by the voltage or E or
V, whichever you're using. And if you're solving for the voltage, then
it would be P for the power divided by I the current. The key
thing to remember in these relationship is that when you're doing one with resistance,
then that's a fixed resistance, like what you get out of a conductor.
It's fixed. When you're doing it for power, it's because you know the
power that you need, right, the power is constant, and that's why
you're doing it, and you're trying to remember that you have to regulate.
If the voltage goes up, the current's got to go down because you need
the power to stay the same. And so that's why that one is inversely
proportional. So with that said, I guess we can go through some examples
here to just kind of hammer some of this home. First one, listen,
okay, so let's just talk Ohms law. So the Ohms law again,
formula will be using to find current because that tends to be what the
question was about the current. Why does the current change or why does what
does it do what it does? So under Ohm's law, the relationship between
the voltage, current, and resistance in the electrical circuit is basically, again
to solve or the eye or amps, it would be the voltage divided by
the resistance and this would be a fixed resistance whatever those resistance values are.
So what this equation tells us is that the current, which is represented an
eye is directly proportional to the voltage for a given resistance value. So the
resistance value did not change. Okay. Also, current is inversely proportional to
resistance for a given voltage. Okay, So that's what we get. So
that's when you see proportional. So the first one that's proportional has to do
with voltage and current for a set resistance value, that didn't change. However,
when it comes to current and resistance, they're inversely proportional for a given
voltage. Okay. So that's a key things that depending on how you write
to how you do the equation. Now, when it came to power,
okay, the power formula relates to power voltage and current, and the first
thing that we do we want to find power. Then we just simply take
the voltage times the current, and that gives us what the power is.
But what is the P. The P is the product of the voltage and
the current. That's what creates the power. Now, for a fixed power,
whatever that wattage may be, whatever that va maybe it's fixed. So
if the voltage actually increases, the current must decrease in order to keep the
product consistent, so to keep the same level of power, So you have
to make an adjustment. That's why they're inversely proportional. Okay, Okay,
so let's talk and so let's even go deeper, because I want to make
sure that everybody was clear in my examples of ohms law. Okay, so
let's talk about that direct proportionality of voltage and current. So when the resistance
itself is fixed, means as a conductor are low. Whatever the resistance may
be, and if it's on an exam, it's just a fit a fixed
value of resistance that somebody gives you, whatever it may be. Okay,
so many ohms of resistance. Okay, So when that ohms omeric value of
resistance is actually fixed amount, the relationship between voltage and current is, like
we said, it's direct. So when you increase the voltage, So when
you increase the voltage in the circuit with a fixed resistance value, whatever it
may be, you are increasing the electric potential difference, which pushes more electrons
through the conductor, thereby increasing the current. So that's why you have that
proportionality, that direct proportion, because if you have a certain amount of resistance,
right and you increase the voltage, then you're trying to push more electrons
through the current, I mean through the conductor, and that means you're going
to increase the current, the amount of current that's being drawn right now.
You decrease the voltage, then that means conversely, when you decrease the voltage,
the electrical potential difference is reduced. As a result, fewer electrons,
if you will, are being pushed through a conductor, and when you're pushing
less electrons through a conductor, you're decreasing the current. Okay, makes sense,
all right. Let me give you an example. So let's just do
a fixed value. Let's say we have ten homes. So again we have
a fixed resistance ten homes, whatever it may be. Maybe this is how
you get it on an exam. You got ten homes, and let's keep
it simple. Let's just say it's ten volts. So you can see how
this works the nice round numbers. So in order to find the current,
and I have a fixed resistance of ten homes, and I'm applying the voltage
of ten volts. Then remember what our example is. It would be the
voltage divided by the resistance. So it's ten volts divided by ten holmes is
one ampire. But now if I increase that voltage to twenty volts, and
I do twenty vaults divided by ten, now the current has increased to two
ampiers. Again, I have more voltage, right, more voltage, which
is more pressure pushing through the same resistance to current flow. And now my
current is going to go up, So the current doubles because the voltage doubleday.
And this is all assuming that that resistant actually stays is the same Okay
in my analogy in this example. Okay, now taking this one step,
but that's how that works. Okay, if you take it to the next
thing and say, okay, well, explain the inverse proportionality of voltage and
current if the power is the same. So we're talking now a power equation.
If the power is fixed whatever that power value may be hundred hundred watts,
six hundred watts, whatever it may be, VA, whatever it may
be. So when power is fixed, the relationship between voltage and current is
in verse. Okay, and so we can explain this this out. So
first of all, to find power, we all know that define power,
it's voltage times the amps and that's how we get power. Okay, that
nice old you know P I E wheel. Okay, put your finger over
the top P then you got p I E or p A V if you
like to use V instead of E. Doesn't matter. So in that scenario,
it's vaults voltage times the current and that gives you the power. Okay.
So one of the things remember is in this scenario, since we're doing
a power a fixed power value for whatever the load may be for power,
when you increase the voltage while maintaining that same level of power, so the
power is not changing. It's whatever the work is you need done, six
hundred watts or whatever it may be. So when you increase the voltage,
the current must decrease. Why this is well, this is because the product
of voltage in current must remain constant. So higher voltage means each unit of
current carries more energy, so you need less current to deliver the same total
power. So in order to adjust it, we have to drop down.
Okay, the current will come down. Okay. Now if you decrease the
voltage, then when increase the voltage, the current must increase to maintain that
same power level, that same wattage. That's necessary. So lower voltage means
each unit of current carries less energy, so you need more current to deliver
what the same total power. Okay. So that again why it's inversely proportional,
is because you lower the power, then you need you get more current
because you're trying to maintain the same power level. You rise up the voltage,
you're going to have to lower the current in order to maintain the same
power level. You get what I'm saying. So that's why they're called inversely
proportional. Okay, So let's those some examples in there of let's show you
how this works. If I've got a hundred watt load and it's a fixed
load, whatever the load would be one hundred watt lamp or whatever it may
be. If you have one hundred watts, now if you apply ten vaults
to that, what will be the current. Well, in this case,
we're going to use the of the P the PIE or PIV depending on whether
you use V or E for your voltage. If I'm solving for I,
which is the current, then that leaves me the P which is the wattage
divided by the E or the V which is the voltage. So that would
be ten one hundred watts divided by ten volts, and that's going to get
ten ams, right, and that's going to get that's what my amps are.
Now, the wattage doesn't change. The wattage doesn't change, So to
do the math, if I increase the voltage to twenty volts, what will
the current be? Well, the wattage did not change, so I have
had to do one hundred watts divided by two hundred volts gives me five ams,
right, So it makes sense. Now we can verify all this.
If you're saying, well wait a minute, Paul, is that going to
give me the same level of power? Absolutely, So let's go back to
the power equation P equals E or V times I. So now that we
solve for I which is the amps, we can go back and verify all
this. So remember, the power didn't change, it's still one hundred watts.
So if I do this, and the first one was ten volts,
we do ten times I, which is the current, So ten times ten
is one hundred. But now go to the same equation where the voltage is
twenty, so we do twenty. Okay times five equals one hundred. So
see the amps had to come down in order to maintain the same level of
power. And if one hundred watts is what we need and that's what the
load is, then it makes sense. So in the field, what you're
seeing is with transformers, it's it's va, which is synonymous with power.
That's what we use the most. Right, we're using a power formula where
that's what we're really doing. We're not so much using the resistance formula.
But just be prepared because you could get a pure resistance question on an exam,
and you as long as you understand the concepts of the power wheels and
the Ohms wheels and the formulas, you're going to be Okay, You're going
to be fine. Just remember the current has because the voltage doubled, assuming
the power stays the same. Okay, hope that makes sense. So then
again that takes us back to the differences, and I'll just end it on
this to kind of relock this into your mind. With you're dealing with Ohm's
law, you're focusing on a relationships that has to do with voltage, currents,
and resistance. And if the resistance is fixed, like in a conductor,
let's say, then when you increase the voltage, it directly increases the
current. Why, because you're increasing the voltage, you're increasing the pressure,
so you're pushing more current means you're driving more electrons through a conductor, So
the resistance didn't change. So by doing so, by increasing the voltage,
it's going to result in increasing the current that's flowing through it. Okay,
So when it comes to the power formula, the relationship is a little different.
It's between voltage, current and power versus resistance. Power. Now,
if the power is fixed, whatever that may be eight hundred you know,
maybe it's eight thousand watts for like a range or or whatever it may be.
If that power is fixed, then you're using a power formula. So
increasing the voltage means that each unit of current carries more energy, so less
current is needed to deliver the same power level. That way, that means
that the current drops, so conversely, decreasing the voltage means it each un
and it carries less energy, so more current is needed and that's why the
current goes up. So you drop the voltage down, it's going to need
more current. It's going to go up. That's why they're inversely proportional.
But you have higher current, excuse me, you have higher voltage, then
they don't need as much current. It's going to go down in order to
maintain the same power level. You with me, hopefully you're following along.
So to summarize it at the end here, voltage in current, when it
comes to Ohm's law, when you have a fixed resistance, you increase the
voltage increases the current. Decreasing the voltage decreases the current. Okay, So
they're directly proportional. When it comes to resistance in current okay, which is
not voltage and current, but resistance in current with fixed with the fixed voltage
means the voltage doesn't change, it's the same voltage. Then increasing the resistance
will decrease the current, and decreasing the resistance increases the current. So you
increase the resistance, you will decrease the current. You decrease the resistance,
you will actually increase the current, and that's if the voltage stays the same,
okay, it's not changing, okay. And that differs from voltage in
current because we're increasing voltage in the resistance and current. That's inversely proportional because
what we're changing here is not the voltage. What we're changing is the resistance,
and that's going to affect the current. And then of course the power
equation. We're dealing with voltage and current when it's fixed power. So when
you have a fixed power value, which is probably what you're using the most,
when you're increasing the voltage, it's going to dease decrease the current.
Right When you increase the voltage, you're decreasing the current, and when you,
of course decrease the voltage, you're increasing the current. So increasing voltage
decreases current, okay, increasing the vultgeage decreasing the voltage increases the current.
So that's why they're inversely for proportional. Did I say that proportional? You
get it? Okay, Hopefully that makes sense. It is tough to kind
of grasp all these things in I guess the analogy. I like to leave
people with the thought of the waterflow. Again, the pipe size or the
conductor size. The resistance is typically fixed, it varies depending on the size
of the conductor. The different resistances to current flow based on whatever size you
choose, the bigger it is, the lower resistance to current flow. It
kind of correlates to Chapter nine, Table eight, where you see a smaller
conductor has higher resistance per thousand feet than a larger conductor. Think of that
the same thing as a big water pipe versus a smaller water pipe. Okay,
thinking of it that way. Thinking of voltage as pressure, okay,
think of the voltage is pressure like a water hose, the amount of pressure
the fauset, how how much you open it versus whether it's opened halfway or
all the way, changing the vault pressure current. Think of current. The
analogy in a water pipe is the flow of the water, right, and
so it depending on how much it flows, is the level of current that's
flowing. Okay, those type of things all right, Hopefully that's made it
a little simpler to understand. I just need you to understand for an exam.
Make sure to separate these out. If you have a wattage value,
you're going to use a power formula. If you've got a resistance value.
You're going to be doing Ohm's law, and it would basically be a E
I R. If you're doing a power it's going to be P I E
right, the E being the voltage, the P being the power, I
being current in that scenario, in the in the E I R, the
E being the voltage, the I being the current, and the R being
the resistance in ohms omeric omega value. Okay, all right, anyway,
kind of a longer podcast on theory. Hopefully you got it. That's about
the best I can do it in a podcast. You can gree to disagree,
and if you don't like it, I look forward to hearing your video
explaining it or a podcast explaining it better than I did. Until next time,
folks, they say, God bless them. We'll catch you on the
next Let's Ask Paul podcast